Few reports have examined the effects of metal exposure at larvae stages on reproduction in nematode Caenorhabditis elegans, an alternative model for chemical screening. In the present study, four metals (Pb, Hg, Cd, and Cr)were selected to investigate the effects that metal exposure has at different developmental stages (L1, L2, L3, L4, and young adult) on the reproduction of this test species. Larval nematodes were more sensitive to reproductive toxicity as demonstrated by altered brood size and generation time versus young adult nematodes. L1-larval nematodes showed the greatest susceptibility. Brood size was significantly correlated with concentrations of all examined metals, and generation time was correlated with concentrations of Pb and Hg. Hg exposure at the L1-larval stage induced the most severe reproductive toxicity among the examined metals; furthermore, the reproductive toxicities induced by 4 h metal exposure at the L1-larval stage were largely comparable to those from 1 d of metal exposure at the L4-larval stage. These results indicate that nematode reproduction is sensitive to adverse effects of several toxic metals at micromolar concentrations and specific developmental stages.